Apparatus for withdrawing a casting from a mold

ABSTRACT

A method and apparatus for withdrawing a casting from an openended mold. The apparatus comprises a starter bar connected to a platform movable along platform guides, and a platform propelling mechanism. The apparatus has electrical connections through the starter bar, and it is capable of precise control. The method comprises inserting a starter bar in the mold, starting the casting process, connecting the product to the starter bar, withdrawing the product and severing the product from the starter bar.

United States Patent Abarotin et al.

. [451 Mar. 21, 1972 [54] APPARATUS FOR WITHDRAWING A CASTING FROM A MOLD [72] Inventors: Eugene V. Abarotin; Thomas E. Nicely,

both of Franklin Township, Westmoreland County; Robert A. Wilshire, Jr., Monroeville Borough, all of Pa.

[73] Assignee: United States Steel Corporation [22] Filed: 'May 22, 1970 [21] Appl.No.: 39,749

3,548,920 12/1970 Torban et al ..l64/274 X FOREIGN PATENTS OR APPLICATIONS 763,970 12/1956 Great Britain ..164/282 1,113,066 8/1961 Germany ...l64/282 1,508,943 1 1/1969 Germany ..164/263 Primary ExaminerRobert D. Baldwin Assistant Examiner-John E. Roethel Attorney-Ralph H. Dougherty [57] ABSTRACT A method and apparatus for withdrawing a casting from an open-ended mold. The apparatus comprises a starter bar connected to a platform movable along platform guides, and a platform propelling mechanism, The apparatus has electrical connections through the starter bar, and it is capable of precise control. The method comprises inserting a starter bar in the mold, starting the casting process, connecting the product to the starter bar, withdrawing the product and severing the product from the starter bar.

6 Claims, 6 Drawing Figures Patented March 21, 1972 3,650,315

5 Sheets-Sheet 1 9 4a 5. l g; 3 25 a 21 FEW IIVI/ENTORS EUGENE ABA/P077, THOMAS E NIGEL) 8 ROBERT A. WILSH/RE JR.

Attorney Patented March 21, 1972 3,650,315

5 Sheets-Sheet 2 FIG. 2

INVENTORS E UG'ENE l./ ABAROT/N, THOMAS E. N/CELY 8 ROBERTA. W/L SHIRE JR.

Alfor ney Patented March 21, 1972 3,650,315

5 Sheets-Sheet 5 F/(i a INVENTORS EUGENE u ABAROTl/V, moms E NICEL r 8 ROBERT A. WIL SHIRE JR.

a k/zwfE/l w-k.

A from 0 Patented March 21, 1972 FIG. 4

5 Sheets-Sheet 4 D N INVEN TORS EUGENE u ABAROTIN, moms E. lV/CEL r a ROBERT A. m1. SHIRE m.

[Judi/ A flamey APPARATUS FOR WITHDRAWING A CASTING FROM A MOLD This invention relates to an improved method and apparatus for withdrawing a cast product from an open-ended mold.

Although our invention is not thus limited, the apparatus is particularly advantageous as applied to the plasma-arc cold mold process of semi-continuously refining steel or other metals. The plasma-arc cold mold process is especially suitable for producing ultra-high purity steels in elongated shapes other than rounds or ovals.

In the conventional plasma-arc cold mold process, a starter bar is positioned vertically in a water-cooled mold. The lower portion of the starter bar protrudes downwardly from the bottom of the mold. A rack suitable for engagement with a pinion gear is affixed to the starter bar. The amount of travel of the bar and thus the ultimate length of the product is limited by the length of the rack. Normally an argon-filled cooling chamber is provided beneath the mold. The inert argon atmosphere assists in purging of the furnace at start-up, and counteracts back diffusion of oxygen and air into the chamber. The product remains in this chamber until it has been cooled to a sufficiently low temperature to be removed. The rack on the starter bar cannot enter the cooling chamber, thus further limiting the length of the product. If the casting expands and sticks in the mold, the rack and pinion may cant and also jam. Another problem in the plasma-arc cold mold process is that electrical ground connections through the mold flange sometimes cause cracks to develop in the weld between the flange and the mold body.

It is the primary object of our invention to provide a withdrawal method and apparatus capable of withdrawing a casting from an open-end mold without jamming the casting in the mold.

It is a further object to provide a withdrawal mechanism in which the electrical power connections are arranged to avoid causing cracks in the weld between the mold flange and mold bod It is another object to provide a withdrawal method and apparatus capable of operating at a variable rate of withdrawal.

It is another object to provide a withdrawal method and apparatus that will impart no twisting moment to the mold or other critical components.

It is another object to provide a withdrawal apparatus capable of positioning a starter bar in an open-ended mold as well as withdrawing it therefrom.

It is another object to provide a withdrawal apparatus adaptable for detaching a cast product therefrom, without severing electrical connections.

In the drawings:

FIG. 1 is a side elevation, with parts broken away, of a plasma-arc cold mold furnace, its associated feed mechanism, and our invented withdrawal apparatus.

FIG. 2 is a horizontal cross section of the withdrawal apparatus taken along line IIII of FIG. 1.

FIG. 3 is a partially sectioned elevation view of a withdrawal platform embodied in our apparatus in the lowered position.

FIG. 4 is an elevation view of the withdrawal platform in the raised position.

FIG. 5 is a plan view of a withdrawal drive mechanism taken along line V-V ofFlG. 1.

FIG. 6 is a side view of the starter bar, partially in section.

Referring now to FIG. 1, a plasma-arc cold mold furnace'll) includes a water-cooled furnace chamber 12 and a watercooled mold assembly 13 in which flange 14 is welded to the mold 15. The bottom of the furnace chamber is closed by flange l4 and starter bar 16. One or more plasma-arc torches 17, each consisting of a constricted nozzle containing a cathode, are disposed in the upper part of the chamber 12 with their lower ends directed to a pool of molten metal 18 in the mold. A feed bar 19 of the metal to be remelted is suspended in a mechanism 20 in the upper portion of the chamber 12 whereby it is continuously advanced toward the mold as it is melted by heat from the plasma-arc.

In the melting process the molten metal pool serves as the anode. After the arc has been struck, the feed bar is propelled toward the pool 18. The pool is contained at its sides by the water-cooled mold assembly 13 which is open at both ends and serves as a caster. The feed bar 19 is heated by radiation and convection and melted, and the resulting molten metal drips into the pool which is supported at its bottom by the starter bar 16. A solidified product '21, which is formed from the molten metal pool 18, is withdrawn at a rate governed by the melting rate.

The plasma-arc cold mold re-melting process described thus far is conventional and similar to the processes disclosed in Gage U.S. Pat. No. 3,147,330 and Dukelow et al., U.S. Pat. No. 3,496,280.

The withdrawal apparatus of our invention continuously removes the product from the molds as it is cast. The apparatus comprises exit guide rolls, a starter bar, a withdrawal platform, platform guides, and a product removal mechanism.

Water-cooled guide rolls 22 are mounted directly beneath mold 15 to prevent damage to the mold caused by excessive lateral forces during casting or product withdrawal. We use two sets of rolls 22a and 22b on the wide dimension of the product and one set of rolls 22c on the narrow dimension. Each guide roll 22 is journaled for rotation in pillow blocks which are fixedly attached to the supporting structure 25. Each roll 22a and 22b is provided lateral support by its associated backup roll 26a and 26b respectively. Rolls 26a and 26b are journaled for rotation in housings 27. The backup rolls, the bodies of which are shorter than the bodies of the guide rolls, enable each water-cooled roll to withstand extremely high lateral forces. Beneath the guide rolls, we position two retaining spindles 28 and 29. Spindle 28 is mounted on pivotal frame 30, which can swing upwardly. Spindle 29 is fixed in its housing. Each spindle is covered by a rotatable sleeve 31, the internal diameter of which is slightly greater than the external diameter of its associated spindle. The sleeve expands when heated, increasing the gap between the spindle and its sleeve. This improves the convective cooling rate of these components by allowing an increased volume of air to pass through the sleeve.

The starter bar 16, as shown in FIGS. 1 and 3, includes a shell 32 of rectangular cross section, to the upper end of which is welded a solid block 33 of steel substantially identicalin composition to that of the feed stock. A horizontal shaft 34 is fixed to the shell near its lower end. A vertical slot 35 is cut in the wall of the shell near the top, and a bar 36 is welded to the interior of the shell across this slot. Near the bottom of the starter bar is an electrical connection 37 having jumper terminals 38.

Withdrawal platform 40, shown in FIG. 3, is a rectangular structure comprising a top plate 41 and bottom plates 42 spaced apart by and secured to longitudinal beams 43. Split pillow blocks 44, which house starter bar shaft 34, are removably attached to top plate 41. Platform 40 has clearance holes 45 to allow platform guides 46a and 46b, and heat shields 47a and 47b to pass therethrough. Ball screws 48a and 48b are rotatable in stationary ball nuts 49, which nuts are secured to platform 40 by trunnions 50 which are housed in pillow blocks 51. The trunnions allow a small transverse deflection of the withdrawal platform which prevents binding of ball nuts 49 on the ball screws. Twelve roller bearings 52 are mounted on the platform, six at each end of the platform, three of the six fixed to the top plate 41 and three fixed to bottom plate 42. The roller bearings, which bear against the platform guides 46a and 46b and are vertically movable therealong, reduce the magnitude of lateral forces acting on the ball screws.

The platform guides 46a and 46b are suitably made of I square tubing fixed at their upper ends to a mounting platform 53 (FIG. 4), and confined at their lower ends by guide pins 54. The guide pins are fixed in mounting base 55. The guides are free to move along the guide pins, as is necessary to compensate for the expansion caused by loading and temperature changes.

I operating floor and supports all drives and screw bearing housings. The upper ends of ball screws 48 (FIG. 4) are journaled in thrust bearings 60 carried by platform 53. The lower end of each ball screw carries a bronze bearing 63 (FIG. 3) that floats vertically in housing 64 fixed to mounting base 55. The ball screws are always kept in tension by the load, and, since they are fixed only at the top are free to expand under variations of temperature and load.

The ball screw drive system (FIG. 5) comprises a variable speed motor 70 with a double-output shaft 71, each end of which is coupled to a respective ball screw through couplings 72, shaft73, coupling 74, horizontal right angle gear box 75, coupling 76, shaft 77, coupling 78, vertical right angle speed reducer 79 and coupling 80 (FIG. 4).

The vertical reducers 79 are protected from the heat radiating from the hot product by heat shields 81 (FIG. 4) which are made of a reflective sheet metal. Reducer base 82'has an annular groove through which cooling water flows to provide additional protection from heat.

A photo cell 85, mounted on structure 25 beneath guide rolls 22 (FIG. 4), is connected to a switch (not shown) which stops motor 70.

The product removal mechanism (FIG. 1) consists of a means for lowering the product and a-product receiving unit. We use a power winch 87, cable 88, snatch block 89 and safety hook 90 as the lowering mechanism. The receiving unit is a slab buggy 92.

In operation, the stater bar l6'is placed in a vertical position and inserted into the lower end of mold cavity by starting motor 70, which drives ball screws 48 and lifts platform 40 toward its raised position, shown in dotted lines in FIG. 1. Thus the solid starting section 33 of the stater bar is positioned at the desired height in the mold. The space between the starter bar and the mold is sealed with asbestos rope. Chamber 12 is then purged of air and filled with argon. The torches l7 are energized and melt a portion of the starting section 33 of the starter bar 16 forming a molten metal pool 18. The feed bar 19 is then fed downward toward the pool by mechanism 20, is melted by the oscillating torches and fills the mold cavity until it reaches the desired level. At this time the withdrawal process is initiated. Variable speed drive motor 70 is started and through its associated double-output shaft, couplings, gear boxes and speed reducers rotates ball screws 48 causing withdrawal platform 40 to move downward withdrawing the starter bar from the mold and with it the partially solidified product 21. The rate of withdrawal must correspond to the rate of melting of the feed stock in order to maintain a constant molten metal level within the mold cavity. The product is withdrawn until the maximum length of cast slab is obtained or until the desired length of product is reached. As the product leaves the mold, it is supported by water-cooled exit guide rolls 22. When the end of the product passes the lowermost guide roll, photo cell 85 delivers a stop signal to drive motor 70, which ceases operation thus terminating product withdrawal.

After the tail end of the product passes the exit guide rolls, it is still supported by retaining rolls 28 and 29. Hook is then attached to bar 36 (FIG. 6) in the tubular portion of the starter bar. Retaining roll 28 is moved up and out of position by angular rotation of pivotal frame 30, thus freeing the product to rotate about shaft 34. Power winch 87 is activated lowering the product on to slab buggy 92 into the position shown in dotted lines in FIG. 1. The cast product 21 is severed from the starter bar 16 by any convenient means, such as burning or sawing. Care must be taken that a sufficient amount of solid material 33 remains above to the tubular portion 32 of the starter bar to begin a new cast. Severmg the product does not sever the electrical connection, for when the bar is replaced in the mold cavity and the torches are energized, the electrical circuit is again completed. The starter bar is then returned to the vertical position by operating the winch, raised into the mold by operating the motor 70 and a new cycle is begun. We have found that when the starter bar is used as the path for the electrical return, the weld between the mold and the flange, as well as the starter bar and the product, show no tendency toward cracking or other detrimental effect, provided all connections are solid.

It can be seen from the foregoing that we have invented an improved withdrawal mechanism capable of operating at a variable rate of withdrawal, not subject to jamming, having power connections through the starter bar, and which does not cause cracks to develop between the mold and the flange. The apparatus is capable of precise withdrawal of a casting without the necessity of precise alignment with the casting.

We claim:

1. Apparatus for withdrawing a partially solidified elongated metal product from an open-end mold, said apparatus comprising:

a fixed base;

a withdrawal platform;

means carried by said base and connected to said platform for raising and lowering said platform;

means for maintaining said platform in perpendicular relation to the product as the platform is raised and lowered, comprising at least two guide bars and two 'pairs of horizontally opposed, vertically spaced rollers acting said guide bars perpendicularly to each other;

a starter bar; and

means for pivoting said starter bar and said product from a vertical to a horizontal position when said platform is in a lowered position, said means for pivoting being mounted on said platform, whereby said platform remains stationary when said starter bar pivots.

2. Apparatus as defined in claim 1 in which said first-named means includes ball screws, the lower ends of which are journaled to said base, ball nuts fixed to said platform, and a drive means connected to said ball screws.

3. Apparatus as defined in claim 2 in which said drive means is a variable speed motor.

4. Apparatus as defined in claim 1 in which said starter bar comprises an upper section of a solid block of metal substantially identical in composition to that of the desired product, a lower section of a structural shape, and a horizontal shaft.

5. Apparatus as defined in claim 4 in which said starter bar has integral electrical connections to provide a current path to the product.

6. Apparatus as defined in claim 4 in which said starter bar includes means for attaching a hook thereto. 

1. Apparatus for withdrawing a partially solidified elongated metal product from an open-end mold, said apparatus comprising: a fixed base; a withdrawal platform; means carried by said base and connected to said platform for raising and lowering said platform; means for maintaining said platform in perpendicular relation to the product as the platform is raised and lowered, comprising at least two guide bars and two pairs of horizontally opposed, vertically spaced rollers acting said guide bars perpendicularly to each other; a starter bar; and means for pivoting said starter bar and said product from a vertical to a horizontal position when said platform is in a lowered position, said means for pivoting being mounted on said platform, whereby said platform remains stationary when said starter bar pivots.
 2. Apparatus as defined in claim 1 in which said first-named means includes ball screws, the lower ends of whIch are journaled to said base, ball nuts fixed to said platform, and a drive means connected to said ball screws.
 3. Apparatus as defined in claim 2 in which said drive means is a variable speed motor.
 4. Apparatus as defined in claim 1 in which said starter bar comprises an upper section of a solid block of metal substantially identical in composition to that of the desired product, a lower section of a structural shape, and a horizontal shaft.
 5. Apparatus as defined in claim 4 in which said starter bar has integral electrical connections to provide a current path to the product.
 6. Apparatus as defined in claim 4 in which said starter bar includes means for attaching a hook thereto. 